Toll switching telephone system



May 1, 1951 HQ w. BALzER TOLL swITcHING TELEPHQNE SYSTEM .Filed Sept. 24, 1947 l2 Sheets-Sheet l H. W. BALZER TOLL SWITCHING TELEPHONE SYSTEM May 1, 1951 l2 Sheets-Sheet 2 Filed Sept. 24, 194'? INVENTOR. Harvey W Balzer BY` g/WM, 00.1% QM/ ON met@ s/m0 May 1, 1951 H. w. BALZER TOLL SWITCHING TELEPHONE SYSTEM 12 Sheets-Sheet 5 Filed sept. 24. 1947 Ams,

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Filed Sept. 24. 1947 May l, 1951 May l, 1951 H. w. BALzER TOLL SWITCHING TELEPHONE SYSTEM l2 Sheets-Sheet 6 om r @om w e Em I @mm mw. @.SOH mm2 W. avv'. V m W mme mow YM. B @5 Y .XE zz Y No@ w i .W llo o lo lmummo mw O im ma MW ibo mu. No@ .T dud MV @www ma mm uw @om lm /llw www ,mms- 4 r @N5 im; mf llo AV .50 49mm@ NN@ Oww NNO Ilo H- dmlowulo Mw lo @www vwwxwu ,NNE BB Aha@ @81mm .3S .X2 m8 f S mz: Jl Om@ Nwwwre l who ,momo .`-rl|||||||4L May 1, 1951 H. w. BALzER TOLL SWITCHING TELEPHONE SYSTEM 12 Sheets-Sheet '7 Filed Sept. 24, 1947 N@Nm r M P. A 52N 135 m m VM-NO A 12H! N nD :25 l E N5 m w. @E2 N5 w. w m o23 EL H M @ci Mww .228 mfli.. @i ON Urmlmw mi2 P28 W 02.25 E28 @252.2 322 222. 8E s iblomlmm EMI @wh 222m :lw @MEW :mvg w2 E @2 @E @26 EMME l m35 c 5222 NQ Ho NS JL $52 N: SEO 5 5 NS b |\|0| :AAAI .m22 im 26 o n NNE l Iloll O lo ON 9&0 E25 m N @N2 .228 d2 @S @I lo May 1, 1951 H. w. BALZER TOLL SWITCHING TELEPHONE SYSTEM 12 Sheets-Sheet 8 Filed Sept. 24,1947

Harvey W Balzer A12 sheets-sheet 9 H. W. BALZER TOLL SWITCHING TELEPHONE SYSTEM AINS- INVENToR. Harvey W. Balzer oom .Eo mz] nick mmm Filed Sept. 24. 1947 May l, 1951 H. w. BALzER 2,550,755

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INVENTOR Harvey W. Balzer 1'2 sheets-sheet 11 IIQIII ET/m H. W. BALZER TOLL SWITCHING TELEPHONE SYSTEM May 1, 1951 Filed sept. 24, 1947 l2 Sheets-Sheet l2 H. WQ BALZER TOLL SWIIfCI-{ING TELEPHONE SYSTEM May 1, 1951 Filed sept. 24, 1947 Patented May 1, 1`951 Harvey W. Balzer, Downers Grove, Ill., assigner to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application September 24, 1947, Serial No. 775,818

` 41 claims. (o1. 179-27) The present invention relates to telephone systems, and more particularly to such systems of the tollswitching type.

A toll switching telephone system usually comprises an oilice provided with a toll board and a plurality of first toll line circuits accessible thereto, an exchange provided with a plurality of second toll line circuits and a corresponding plurality of associatedtoll iirst selectors accessible thereto, and a corresponding plurality of toll lines interconnecting the corresponding pairs of rst and second toll line circuits. Also the exchange normally comprises Vtrunks and toll transmission selectors accessible to the toll rst selectors, combination connectors accessible to the toll transmission selectors, and subscriber lines accessible to the combination connectors. In this l system the toll iirst selectors are necessary to complete toll connections to the trunks, which do not ordinarily require the supply thereto of transmission battery; while the toll transmission selectors are necessary to complete toll connections,

ythrough the combination connectors, to the subscriber lines, which ordinarily require the supply thereto of transmission battery. While this arrangement is entirely satisfactory in operation, and necessary in large exchange networks, it requiresranks of toll first selectors and ranks of toll transmission selectors, notwithstanding the fact that in a given exchange the total number of outlets may be relatively small.

Accordingly, it is a general object of the present invention to provide a toll switching telephone system comprising a minimum number of ranks of automatic switches in the toll switch train.

Another object ofthe invention is to provide in a telephone system of the type noted, a combination toll-first and toll-transmission selector.

Another object of the invention is to provide a combination switchethrough and toll-transmission selector capable of the two operatiom mentioned in response `to one digit and totwo digits respectively, whereby the normal directory nurn-Y bering scheme is not disturbed by the substitution in 'the jtoll switch train of the combination selector for the usual tandem related .toll iirst selector and toll transmission selector.

l. Another Object of the invention is to provide anv auxiliary toll selector of improved connection and arrangement, embodying both split-level and full-level'trunk-hunting and busy facilities.

p. Anotherobject of the invention is to provide an improved selector of the combination one digit andtwo digit type embodying facility for return- 2Y ing a delay-digit signal during trunk hunting operation. Y Y Y A Another object of the invention is to provide in a switch train including first and second tandem related automatic switches, an improved arrangement governed by operation of the second switch for selectively setting the final position of th rst switch. f

v A'further object ofthe invention is to provide the nal connection between the iirst and secondV switches.

A further object of the invention is to provide in a toll switchingv telephone system involving an office and an exchange interconnected by a trunk line, improved terminating line circuits arranged to trunk toll calls over the trunk line from the oiiice to the exchange and to trunk C. L. R. calls over the trunk line from the exchange to the oiiice.

A further object of the invention is to provide a toll line circuit embodying improved control and supervisory circuit facilities.

' A still further object of the invention is to provide a toll switching telephone system involving a plurality of oiiices and exchanges and embodying improved trunking and supervisory facilities permitting the direct completion of toll calls from a toll board without multiple handling at one or more other such toll boards.

A Further features of the invention pertain to the particular arrangementv of the circuit elements of the system, whereby the above-outlined and additional operating features thereof are attained.

Sect. 1.-The general arrangement of the telephone system The invention, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure l is a schematic diagram of the area served by a telephone system embodying the present invention and illustrating the general arrangement of the apparatus incorporated inV several of', the offices and exchanges thereof; Figs. 2 to l2, inclusive, taken together, illustrate the details of certain of the c apparatus incorporated in the telephone system,

which apparatus has embodiedA therein the fea- Fig. 4, illustrates` the details of one of a liirst group of ytoll line circuits `in the central ofce; Fig. illustrates the details of one of the information trunk circuits in the central oiice; Fig. 6 illustrates the details of one of theauxiliarytoll selectors in the central office; Fig. 'I illustrates the details of one of the ringing control circuits in the central ofce; Fig. 8 illustrates the details of` one of the toll transmission selectors in the central oice; Figs. 9 and 10, taken together, illus-4 trate the details of one of a second group. of toll line circuits in the central oilce; and Figsflland 12., taken together, illustrate the details of oneV of the toll line circuits in the distant exchange.

Referring now more particularly to Fig; 1, the telephone system there illustrated serves an area comprising a distant office I0, a central oice 20, a distant exchange 30 and a remote exchange 40. The vdistant oce I0 is of the automatic type, serves substations of any suitable type, and comprises a manual dial toll board 220; and the remote exchange 40 is of any suitable type, serves substations of any suitable type, and comprises a manual 'toll' board 604. The central oce 20 isof the automatic type, serves substations of any suitable type, andl comprises a manual dial toll board 300; whilethe distant exchange 30 is of the automatic type and serves substations of any suitable type. Specifically, the central office 20 serves a plurality of groups of subscriber substations, one of theV groups including the subscriber substation T20I. The distant exchange 30 serves a plurality o f groups of subscriber substations, one of the groups including the subscriber substation TI20I, and a group of paystations, not shown. The subscriber substation'T2'0i has a subscriber line 202 extending thereto that is provided with an individually associated line circuit 203 of any suitable type; and the subscriber substation T|20| has a subscriber line |202 extending thereto that is provided with an individually associated vline circuit |203 of any suitable type.

The distant office I0 and the central oice 20 are interconnectedV by a group of toll lines, including thetoll line 2|0; the central oce 20 and the distant exchange 30 are interconnected by a group of toll lines Vincluding the toll line II|0; and the central oice 20 and the remote exchange 40 are interconnected by a group of trunk lines including the trunk line 603. The toll lines 2 I0, etc., are of the two-way type terminating in toll line circuits respectively disposed in the distant office I0 and in the central oilce 20, the toll line 2I0 terminating in the toll line circuits 2I5 and 400 respectively disposed in the distant office I0 and in the central oice 20. The toll lines IIIO, etc., are of the two-way type terminating in toll `-line circuits respectively disposed in the central oice 20 and in the distant exchange 30, the toll line |IIO terminating in the toll line circuits 900 and H00 respectively disposed in the central oiice 20 and in the distant exchange 30. The trunk lines 003, etc., are of the one-way type Eterminating in ring-down trunk circuits disposed in the central ofce 20 and at the toll board 604 Ydisposed in the remote exchange 40, the trunk' line 603 terminating in the ring-down trunk cir- Icuit 60| disposed in the central ofce 20.

y The distant oice I0 comprises a local switch train, not shown, the central ofce comprises a local switch train including a plurality of nderselector groups and a plurality of connector groups, not shown; and the distant exchange 30 comprises a local switch train, including a plurality of nder-selector-groups and .-a plurality of connector groups, not shown. Specically, the

' local switch train in the central omce 20 comprises a fourth group of :finder-selector links, including the link illustrated comprising the nder 206 and the selector ZIB'I; which group is provided with adistributor 204, the under 206 having access to the'subscriber line 202 extending to the subscriber substation'TZi, and the.line circuit 203 individually associated with the subscriber line 202 being connected to the distributor 204 by a start conductor C205. Similarly, the local switch train in the distant exchange 30 comprises a fourth group of finder-selector links, including the link illustrated comprising the finder |206 and the selector |201; which group is provided with a distributor |200, the finder |200 having access to the subscriber line |202 extending to the subscriber substation TI20I, and the line circuit I203 individually associated with the subscriber line |202 being connected to the distributor |204 by a start conductor CI 205.

Also the distant orlce I0 comprises a toll switch train including a group of toll transmission selectors, one of the toll transmission selectors being indicated at 22|; which toll transmission selector 22| is individually connected to the toll line circuit 2I5 by a trunk 2I'I extending there'- from. Also the toll line circuit 2|5 is accessible to the toll board 220 via a trunk ZIS extending thereto. Similarly, the central oihce 20 comprises a toll switch train including a group of toll transmission selectors, one of the toll transmission selectors being indicated at 300; whichv toll transmission selector 800 is individually conneet-ed to the toll line circuit 4.00 by a trunk 420 extending therefrom. Also the toll line circuit |00 is accessible to the toll board 300 viaa trunk fait extending thereto. Finally the distant exchange 3Q comprises a toll switch train including a group of toll intermediate selectors, one of the toll intermediate selectors being indicated at I2I5; which toll intermediate selector I2I5 is individually connected to the toll line'circuit H00 by a trunk |2I0 extending therefrom. Also the toll line circuit H00 is accessible to the local switch train via a C. L. R. trunk |220 extending thereto. Further, the toll switch train in the central cnice 20 comprises a plurality of groups of combination local and toll connectors, the fourth group of combination connectors including the combination connector 235 illustrated. Also the combination connector 235 has access to the fourth group of subscriber linesincluding the subscriber line 202 extending to the subscriber substation TESI. Further, the combination connector 235 is accessible to the toll transmission selectors 800, etc., Via a trunk 200; and is also accessible to the selectors 201., etc., via a' trunk 208. Similarly, the toll switch train in the distant exchange 30 comprises a plurality of groups of combination local and toll connectors, the fourth group of combination connectors including the combination connector I2I' illustrated. Also the combination connector IBI? has access to the fourth group'cf -subscriber lines, including'the subscriber line |202 extending'to the combination connectors 235, etc.

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the subscriber substation T| 20| Further, the combination connector |2|1 is accessible to the toll intermediate selectors |2|5, etc., via a trunk |2|6 and' is Valso accessible to the selectors |201, etc., via a trunk |2|8. y

Further, the toll switch train in the central o'iiice20 comprises a group of auxiliary toll selectors, including the auxiliary toll selector 000, and

an associated group of ringing control circuits, including'the ringing control circuit 100; the auxiliary toll selector 000 being connected to the ringingl control circuit |00 individual thereto by the trunk 120. In turn, the ringing control circuitv 100 is accessible to the toll transmission `selectors '000, etc., via a trunk 1|0e'xtending there-V to. IAlso the auxiliary toll selectors 000, etc., have access to the trunks 240, etc., extending to Further, the toll transmission selectors 800, etc., have access to the toll line circuits 900, etc., via trunks 910, etc., extending thereto; and the toll line circuits 900, etc., are accessible to the toll board 300 via trunks 020, etc., extending thereto. Also the auxiliary toll selectors 000, etc., have access to the ring-down trunk circuits 00|, etc., via trunks 002, etc., extending thereto. Also the toll switch train in the central oice l0 comprises a group or" toll' connectors, including the toll connector 105. The toll connectors 105, etc.; are accessible to the auxiliary toll selectors 000, etc., via trunks 100, etc., extending thereto. f

Also the central ofce 20 comprises a group of T. Xtrunk circuits, including the T. X trunk' circuit30| a group of inward trunk circuits, including the inward trunk circuit 300; anda group of information trunk circuits, including the information trunk circuit 500. The T. X trunk circuits 30|, etc., are accessible to the auxiliary tollv selectors 000,' etc., via trunks 302, etc., extending thereto; and are, in turn, connected to the toll board 300 via trunks 303, etc., extending therefrom. Similarly, the inward trunk circuits 304, etc., are accessible'to the auxiliary toll selectors 000, etc., via'trunks 305, etc., extending thereto; and are, in turn, connected to the toll board 300 via trunks306, etc., extending therefrom. Finally, thev information trunk circuits 500, etc., are accessible 'to the auxiliary toll selectors 000, etc., via trunks 505, etc., extending thereto; and are, in turn, connected to the toll board '300 via trunks 5|0, etc., extending therefrom.

Finally, thecentral oiiice 20 comprises a group Sect. z -The apparatus incorporated in the telephone system In the distant'oflce |0, the toll boardV 220 is of the conventional manual dial type, including cord circuits, not shown; the toll line circuits 2 l 5,' etc.,'are identical tothe toll line circuits 400, etc.,ir1 the central oice 20; and the toll transmissionlselectors 22E, etc., are identical to the toll transmission selectors 800, etc., in the central oice 20. In the remote exchange 00,thev toll board 004 is ofthe conventional Vmanual type, including cord circuits, not shown. In the distantexchange 30, the line circuits |203, etc., as well as the distributors |204, etc., are of any suitable'f-types; while the nders 1200, etc.; the selectors' |201, etc., the combination connectors |2| 1, etc., and the toll intermediate selectors |2|5, etc., are of conventional Strowger types. Similarly, in the central office 20, the line circuits 203, etc., as well as the distributors 204, etc., are of any suitable types; while the nders 200, etc., the selectors 201, etc., the toll connectors 105, etc., and the combination connectors 235, etc., are of conventional Strowger types. Finally, in the central oiiice 20, the C. L. R; trunk circuits 230, etc., the T. X trunk circuits 30|, etc., the inward trunk circuits 304, etc., and the ringdown trunk circuits 60|, etc., are of any suitable types. Y

As previously noted, the toll board 300 in the central oflice 20 is of the manual dial type and comprises, as shown in Fig. 3 a numberof cord circuits, including the cord circuit 320 that terminates on a rear plug P32| and a front plug P322'. Also the 'cord circuit 320 comprises a ring rear key X330, a ring front key K33l, a dial rear key E332,` and a dial front key K333, as well as a relay group including a rear supervisory relay R345, a dial relay R350, and a front supervisory relay R355; and also a rear supervisory lamp L334 and a front supervisory lamp L335. Further, the cord circuit 320 is connectible to a headset 320 and to an impulse transmitting mechanism of the dial type 321 disposed at the toll board 300.

The trunk 232 extending from the C. L. R. trunk circuit 330 terminates in a jack J 310 individual thereto at the toll board 300 and is provided with an individually associated answer lamp L31|. Similarly, the trunk 5|0 extending from the information` trunk circuit 500 terminates inV a jack J312 individual thereto at the toll board 300 and is provided with an individually associated answer lamp L313; the trunk 303 extending from the T. X trunk circuit 30| terminates in a jack .1314 individual thereto at the toll board 300 and is provided with an individually associated answer lamp L315; and the trunk 300 extending from the inward trunk circuit 304 terminates in a jack .T310 individual thereto at the t'oll board 300 and is provided with an individually associated answer lamp 41311. The trunk 4| 0 extending to the toll line circuit 400 terminates in a jack J318 individual thereto -at the toll board 300 and is provided with an individually associated busy lamp L319; while the trunk 020 extending between the toll board 300 and the toll line circuit 000 terminates in a jack .1380 individual thereto at the toll board 300 and is provided with individually associated busy and answer lamps L38| and L302 respectively.

Preferably each of the toll line circuits in the first group mentioned is identical to the toll line' circuit 400 which comprises, as shown in Figs. 3 and 4, two repeating coils 300 and 305 and a relay group including. a signal relay R305, a supervisory relay R430, a control relay R440, two re-ring relays R450 and R055, a switch relay R460, a pulse relay R410, an answer relay R415, a dial relay R480, a hold relayR485, a cutthrough relay R490, and a seize relay R000. Preferablyeach of the information trunks is identical to the information trunk 500, shown in Fig. 5, which comprises a repeating coil 510 and a relay group including an answer relay R520, aline relay R525, a supervisory relay R530,a hold relayR540, a recall'relay R550, a jack relay R555, anda recall relay R560.

Preferably each of the auxiliary tol-l selectors aoco-,75e

iScdentical to the-auxiliary toll selector 688v that` comprises, yas .shownin Fig.- 6, a relay group ,includinga busy' relay Rli-I 8, a controlrelay-R828, a line .relay R888,a control relay R888, a hold relay R858, a, test relayv R688, acut-out relay.l

R618,a transfer relayR888, and a step relay R685. Further, the auxiliary toll selectorl 888 comprises a Strowger mechanism 888 prrwidedY with-a wiper setrincluding five wipers 88! Vto 885,

inclusive, a vertical magnet-V M898-ior driving` thev wiper carriage step'by step in the vertical direction; a'rotary magnet M881 for driving the wiper-carriagestepbyA step in the rotary direction, and a release magnet M889 for releasingthe wiper carriage and for-causing it to be re turned to its normalrotary and vertical positions. Alsorassociated with the Wiperrcarriage of the Strowger mechanism 888 lare twoy sets of switch springs S888 and S881 which are operated when the wiper carriage is driven one step in the vertical'direction away from its normal vertical position.; Also associated with the wiper carriage of theStrowger mechanism 888, are three sets of switch springs S818, S818 and that are operatedwhen the wiper carriage isdriveneleven steps in the rotary direction away from its normal` rotary position. A `set of switch springs S834 is. associated with theV wiper carriage of the Strowgermechanism 698 andoperated when the wiper carriage is driven either four or six steps in the .vertical direction away from its normal kvertical position. Finally, two sets of springs S633 andV S835 -are associated 'with the wiper carriage of theStrowger mechanism 898 and operated when the wiper carriage is driven either `rive `orisix steps in the vertical directionv away from its normal vertical-position.

Preferably, eachof the ring-down control circuits is identical to the ring-down control circuit 188 that comprises, asshown in 7, a repeating coil 18| and a-relay groupl including a supervisory relay R138, an answer relay R135, twov control relays R188 andRllli, a timer relay R158, a ring relay R188, a line relay R118 and a start relay R188..

Preferably, each of the. toll transmission-selectors is identical to the toll transmission selector 888 that comprises, asshown inFig. 8, a repeating coil 823 and a relay group including a toll relay R818, a step relay R828, a line relay R825, a digit absorbing relay R838, a hold relay R848, a dry relay R858, a controlrelay R868, a Ytone relay R818, a supervisory relay R815, a transfer relay R888 and a test relay R888. Also the toll transmission selector 888 comprises a Strowger mechanism 88! includingv live wipers 882 to 8855, inclusive, a vertical magnet M881 for drivingV thewiper carriage step by step in the Yvertical direction, a rotary magnet M888 for driving thewiper carriage step by step in therotary direction, and a release magnet M8l8 for releasing the wiper:

carriage and for causing it to be returned to its;

normal rotary and vertical positions. Also, associated with the wiper carriage of the Strowger mechanism 88I are two sets of switch springs S884 and S885 that vare operated when the wiper carriage is driven one step in the-verticaldirec-f tion away from itsnormal vertical position. Also associated with the wiper carriageof the Strow-4 ger mechanism 881 are two sets of switch springs S888 and S881 that are operated when the wiper carriage is driven eleven steps in ,the rotary. direction away from itsY normal rotary position.

Further, a set of switch springs S888 is asso-H ciated `with the wiper carriageoith Siuovvger mechanism 88| and voperated when f thei wiper--l carriage: is vdriven eight: steps in v-the vertical vdirection away fromiits normal vertical position.

Finally, a .set `of.'switchsprings S889 isv associated with' the wiper carriage of the Strowger mech anism-88l and operated when the wiperA carriage' is driven two steps in the vertical direction'away from its normal vertical position'.

Preferably, vveach' ofthe toll line circuits/in the second groupy mentioned is identical -tothe toll line circuit 988 that comprises, :as shown in Figs. 9 'and 10,'a repeating coil 932 anda relay/group includinga ring relayiR8381, two switch Lrelays R888 andR858, a supervisoryrelayRSU, a lineA` Y relay R885,a^ hold relay R918, a'busyre'laylRBB,

a seize relay R988, a call relay A:RI8I8,"a dial relay Rl828, a switch relay Rl838,v a control relay RI888,1.a bridge relay` RI858, a signal relay Ri888, ahold relay R1818, a ring relay Rl888 and` an automatic yring re1ayRl888.

Preferably., each'of the-toll line'circuits iin the group including the 'toll lin'evcircuit l i 88 is identical thereto and comprises, as shown in Figs. 11 and 12a repeating coil |I38"and-a relayi'group including a reverse battery relay-RH I5,` ai line! relay Ri t28, a ring vrelayiRl |25, a switch'relay- R! l8an. end-oi-dial relay Rtl58, a tone relay' R! i88,'a signal relay'Rl |18, a supervisory' relay Rll88, a--hold relay RI'2`38, adialV relay RI248ga ring relayk Rl25'8fa control relay R1268, a cut-'olf relay RI218 and a timer-relayvR'liZl A better understanding of` the connection and arrangement of the apparatus-.incorporated-in the telephone systemwwill be facilitatedfrcm a consideration' of the Sex-tension of callsinvolving the various offices andexchanges.

Sect. s-Locel calls mtie central op' First assuming that ak call is initiated atv the subscriber substation T28l in the central oice 28 that is to be completed locally to 'another sub# scriber substation therein, the line circuit 283 is controlled via the subscriber line 282-in order to' govern operation of the distributor 284 over the start conductor C285; whereby anidle one ofthe links, such for example, as4 that illustrated, is

assigned thereby. The iinder 288 of the 'link illustrated operates to find the subscriber line 282 extending to the calling subscriber substation T28`i; whereby the line circuit 283 'is Voperated in vorder to mark the subscriber line282 as busy to the other links having access thereto. the selector 281 of the link illustrated operates toreturn dial to'neover the subscriber line '282 to thev calling subscriber substation T28 lfwhere-- local connector; whereby4 it operates to select the subscriber line extending to the called subscriber substation. The subsequent-operationy of the se-v lected local connector dependsupon the idle orbusy condition ofthe calledy .subscriber substaf tion .and is in--accordancefwithlconventional'v practice. Also the subsequent completion of thel established connectiom. as well as1the ultimate group;

release thereof, is entirely conventional. In passing, it is noted that in the event all of the p local connectors in the group selected by the selector 201 in response to the first digit dialed at the calling subscriber substation' T20! are busy, [the selector 201 operates to select an idle one of the combination connectors in the same which selected combination connector then responds to the second and third digits dialed at the calling subscriber substation T! in a conventional manner.

Sect. 4.-C'. L. R. calls in the central oli'ice Now assuming that a call initiated at the calling subscriber substation T20! is to be extended to the toll board 300 in the central oiiice 20, a link, such, for example, as that illustrated, is taken into use in the manner previously explained. The subscriber at the calling subscriber substation T20! then dials the single digit 0; whereby the selector 201 responds thereto to select first the group of C. L. R. trunk circuits, including the C.L. R. trunk circuit 230, and then an idle C. L. R. trunk circuit therein. For example, the selector "201 may select the particular C. L. R. trunk circuit 230 via the trunk 23! extending thereto;

wherebyV the C. L. R. trunk circuit 230 creates a calling condition upon the trunk 232 extending therefromucompleting a circuit for illuminating the answer lamp L31! associated with the jack vJ310 terminating the trunk 232 atthe toll board 300. The illumination of the answer lamp L31! at the toll board 300 indicates to the operator thereat that a C. L. R. call is waiting to be answered on the trunk 232; whereby the operator mentioned Vselects an idle cord circuit, such, for example, as

the cord circuit 320 and inserts the rear plug "P32! thereof into the jack J310. When the rear in order to extinguish the answer lamn L31l.

The circuit extending from the calling subscriber substation T20! to the toll board 300 includes the subscriber line 202, the finder 206, the selector 201, the trunk 23|, the C. L. R. trunk circuit 230, the trunk 232, the tip and the ring of the jack J310, the tip and the ring of the' rear plug P32!, the second and fourth contacts of the ring key K330, the second and fourth contacts of the dial rear key E332 and the headset 329 at the toll board 300. Also at this time, va circuit, including the sleeve of the jack J 310, the sleeve of the rear plug P32! and the contacts 3.6!, is completed for 4energizing the winding of the rear supervisory `relay R345; however, the latter relayY does not operate at this time as it is of the marginal type. The-subscriber Aat the calling subscriber substation T20! then advises the operator at the toll board 300 concerning the extension of the toll call or the other toll service required.

Subsequently, when the subscriber at the calling subscriber substation T20! disconnects the C. L. R. trunk circuit 230 is governed; whereby low resistance ground potential is applied therein via the associated conductor in the trunk 232 to the sleeve of the jack J310 in order to complete ua lowlresistance circuit substantially identical to ing the rear supervisory relay R345 completes, at

the contacts 346, a circuit for illuminating the rear supervisory lamp L334 in order to render disconnect supervision to the operator at the toll board 300 When the operator at the toll board 300 then withdraws the rear plug P32! of the cord circuit 320 from the jack J310, the circuit for maintaining operated the rear supervisory relay R345 is interrupted causing the latter relay to restore and extinguish the rear supervisory lamp L334. Also the rst contacts of the jack J 310 are opened; whereby the C. L. R. trunk circuit 230 is released bringing about the release of the selector 201 andthe nder 206; whereupon the line circuit 203 is governed in order again to mark the subscriber line 202 extending to the subscriber substation T20! as idle to the local connectors having access thereto.

Sect. 5.-A call from the toll board in the distant otce to a subscriber substation in the central ojice routed directly from a toll transmission selector to a combination connector Now assuming that a call is initiated at the toll board 220 by the operator inserting a front plug of a cord circuit ,thereat into the jack terminating the trunk 2I6 extending to the tollvline circuit 2!5 in the distant olce l0 terminating the toll line 2!0, the toll line circuit 2!5 is controlled in order to cause ground potential/therein to be removed from the simplex of the toll line 2I0 and battery potential to be applied thereto; whereby a circuit Ais completed for effecting operation of the signal relay R385 in the toll linekcircuit 400 in the central oiice 20. A More particularly, `the circuit mentioned includes the line conductors C2!! andCZlZ of nthe toll line 2|0, the windings 30| of the 'repeating coil'390, the simplex conductor C388, the intermediate winding of the signal relay R385, the impedance element 381 and the contacts 433 and 418, and extends to ground potential. Upon operating the signal relay R365 completes, at the contacts 386, a circuit for operating the pulse relay R410; and upon operating the pulse Irelay R410 completes, Aat thecontacts 413, a circuit for operating the holdrelayR485. Upon operating the holdy relay R485 completes, at the contacts 488, a path for applying ground ,potential to the conductor vC 4Ib lof the trunk 4MB, thereby to illuminate the busylamp L319 associated withthe4 jack J 318` at the toll boardllll in the central oiiice 20 in order to indicate to: the operator thereat that the toll line 2|0 is busy at this time.` Also the'hold relay R485 completes,- at the contacts 481, a circuit for energizingthe. right-handwinding of the answer relayR415, thereby torender the vlatter relay operative when the left-hand winding thereof is subsequently energized and properly poled, the answer relay R415 being of the shunt-field type. Further, the

transmission selector 800; completes, at the con'.- tacts 463, a path forapplying battery A.potential by way of the winding of ,thesupervisory relay R430 to the.EC, .conductor C424 of. the trunk 420.; and interrupts. wh@ @ses @Giani-age l1 normalpath connecting lthe winding ofthe re.ring .relayj R455,to'. the windingsg ofthe repeating co'il395. Also 'the switch .relay R460 completes, .fat `the .contactsll46 I, 462,'466 .and 468; a, path for ,bridging the` leftj-.hand windingxof y.the answer -relayIR'415across 'theline conductors"`C422 and ,T042 I..ofl the trunk' 420;"the" last mentioned path :extending from'jthe line conductor C422..by way of lthe contacts.41|. .and,46 I, one of the windings' cf `the repeatingcoil1395,the contacts468, the .leftghand-winding of. the.. answer relay R415; the ,contacts'4.66Q .theether'winding 3'96..of.'the repeatingcoil 395. and` the contactsl 462Y .to 'the' line, con- ;ductorJC42I. .-.-Also, at.fthis time,the.1ine con- ,lductorsC42 I ,and C422 -oftthe trunk. 42 0 are .con- .inected' by way .oft the. contacts .8 I-I ,L B I4 and fthe .-.windngsf824 of the. repeating. m1111323` and -the upperrand. lower windingsof the.line. relay R025 inlthetclltransmission selector B00 respectively td.battery.andfgroundpotentials Accordinglyra loop circuit is completed for energizing .in series the left-hand winding of the answer relay YR415 :iny the toll line circuit 400 andtheuppernnd '-lower windings ofi'the lineirelay R8251inithe toll 'transmission selector 800 Iwhereby 1 the fanswer -relayRMS does-noteperate' as it' is fnotproperly :poled: whereas the line relayE R825 operates.

Upon roperating-.the line. relay R825 completes, atthe contacts.f82-I; la circuit,rincludingthe convtacts M8-I 8, for :operating -.the hold relay .R84'0; rwhereby tl1e..latter re1ay upon operating completes-at theccontacts .84I, a.multiple= pathffor `.applying ground potential to Ithe .-controlcon- ;d-uctor C423- -of the trunk .420. The-application of.` ground. potential .to `.the control :conductor .C423 .of thetrunk 420 completes acircuit, including the rst-contacts: :of the set of `'switch springs S885, .for energizing .the Alowerwinding' of .the trans- .'ferrelayR880; in. ordertocause-the latter Irelay v.tooperate Uponoperating the transfer relay R880 completes; atthe contacts ,88 I .a,circuit,z including .the contacts 48 I for.. energizing` thelower '.Windingotthe dry relay=R850 whereupon the latter .,relay. operatesshortly thereafter, it. being .of the ,combination fslow-tooperate-:andI .Slow-toreleasetype. .Upon operating `the dry relay R850 .interrnpts,.at the contacts=85 I ,-.the normallycom- .pletedpath for bridging. the condenser 818 across therwindingsf825. .or the repeating. coil-.823; com'- lpletes, e at the; contacts.,852, apath for. short-circuiting .the .upper .winding 825 of the .repeating coil .823; .and interrupts, at .the contacts 853, a normally I,completed .path for .bridging ithe. con- .denser..829 across the windingsz824 of the re- .ipletes,at. the contacts 854, a ci-rcuitVincludingNthe Ycontacts 84 I ,i for operatingthercontrol relay:R850. ,IIpon. operating. the control, relay R8 6.0 interrupts, atlthecontacts I and Il63,..the.normal` connec- ,tions betweentheupper .winding ofthe-tone-relay .R810 ,and ,the .upperandlower -windings of the .s upervisory..re1ay R815. and .the .windings :8250i .the repeating coil .823.;andcempletesatthe con tacts .862 .and 8.64, a connection, including athe .contacts 82.6, between the upper .windingfof Athe izo '12 been' seized and' is .conditioned to respondto'the nrstjdigit received" over the trunk"42 0.

Now assuming that .the present l call vinitiated at thetdllboard 220 in thedistant'oce I0is to Abe extended' to'theY calledifsubscriber' substation `T20I 'in'. the 'centraliciiice .20 directly from' the toll transmission.selector 800ito acomblnation connector, .the operator at .the toll board 220 idials the. proper'v digits comprising the. digits' 2,14, X andX therst'digit v2 and ithesecond digit 4 indicating the route 'mentioned andthe third andiv ttourt-h f idigits `identifying the .line terminal .before .the combination. connector .of .the subscriber line`202 extending .to. the called. subscriber substation T1120I. .More particularly, when .the rstrdigitiz isfdialed .at the calling toll bcard`220 in. the Adistant oiice -..l 0, .battery .potential is -re- .moved-from andground vpotentialis applied to '.thesimplex of theitoll. line 210 uponeachim- .pulse .cf theI first. digit '.2 whereby .the signal relay R385in thetcll linecircuit 400 follows. '.Each time 'thesignal ,re1ay'R385 i restores .and then .i-eoperates, Ait interrupts and .thenrecompletes at. the contacts 386,. the .circuit .for maintaining .operatedthe pulse relay`R410; whereby theilatter .relay fiollows. Each time the .pulserelay R4T0 .restores and them reoperates, it. interrupts .and k.then-recompletes, atthe .contacts .413, the

.circuiti for maintaining operated .the Vhold Vrelay AR485; whereby the latter `relayds .retained lin its operated position duringimpulsing as'it is of ithe. 'slow-ftofrelease type. '.The first .time .the `pulse relay R410 restores .and .then reoperates,

lit completes. and then interrupts, at the contacts .43.5 i

.erating.the.dial.. relay R480; whereby the latter 'relay.operates andremains operatedduring im- 412,.fa.circuit, .includingthe contacts 460, for .op-

pulsing asit isofthe slow-to-release type. Upon .operating .the Vdialrelay R480 completes,.rat the contacts-482, a -path,.including the .contacts 468 and 462, the resistor .483, and theline.. conductor C42I .of the .trunk l42`-,0,..for -short-.circuiting the righthandwinding 396 of the .repeating coil P385 ,inor'derfto improve `impuls-ingover the line' `.conductors C422 and.C4`2I of thettrunk 420. .Alsoy each time .the pulse relay .R41 restores and Ythen- .reoperatea it interrupts `and .then 4recompletes,` atrthe `contacts ..41I, .the loop.circuit. extending' 'between theleft-hand .winding ofthe: answer' re-r lay R`415`in thetoll line circuit. 400 andtheupper and lower .windingsrofgthe line. relay.-R825..inthel toll transmission selector .800 ;y v.whereby Athe line .'Eachtimethe linerelay. R825 .inthe toll trans- `mission. selector 800.,restores..and fthenreoperates, v.it interrupts and .thenrecompletea .at the contacts 821, the circuit .'.for -inaintaining operated Vthehold relay1R840; .wherebythe latterfrel-ay-is .retained in its .operated position during 4impuls-- ing as .it eis of the .slow-to-release type. Also each `time the. line :relay .R825 .-.restores and `then .reoperates it .completes and .then f interrupts, at the contacts .'82'8, a circuit, including `the contacts 8I8, '842 .andl882,.for energizing the -upper .winding .of .the .transfer relay :R880 and :a v.multi- Xple circuit for .energizing the vertical imagnet.

7 5 `the'vertical dlrectionawayrrom ltsnormal 'verticontacts of the setV of switch springs S885 are closed completing a circuit, including the con- ,tacts 841, 899-and 848, the set of switch springs S885 and the contacts 809, for operating the step relay R820; however, without effect at this time.

At the conclusion of the rst digit 2, battery potential in the toll line circuit 2 l5 in the distant oilice is returned to the simplex oi the toll line 210 inorder to retain operated the signal relay R385 in the toll linecircuit i100 in the central oice 20. The operated signal relay R385 retains operated the pulse relay Rl'lil; whereupon the `dial relay R480 restores shortly thereafter, it being of the slow-to-release type. Upon restoring `the dial relay R480 interrupts, at the contactsv 402,r the previously traced path for short-circuiting the right-hand Winding `308 of the repeating coil 395. Also the operated pulse relay Rlii in the toll line circuit 400 retains operated the line relay R825 in the toll transmission selector 088; whereupon the transfer relay R880 restores shortly thereafter, it beingV of the slow-to-release type. Also when the wiper carriage of the Strowger mechanism 801 is driven two steps in the vertical direction away from its normal vertical position, the set of switch springs S389 is operated. More particularly, the second contacts of the set of switch springs S889 are closedto prepare a circuit for operating the release magnet M8 1.0. Upon restoring the transfer relay R888 completes, at the contacts 883, a circuit, including Y the Vcontacts 845, MC812, 834 and 897, and the second contacts of the set of switch springs S880, for operating the release magnet M818. Upon operating the release magnet M8i0 completes, at the contacts M0811, a holding circuit therefor, including the contacts r45 and the set of switch Springs S884; and interrupts, at the contacts M0812, the previously traced original operating circuit therefor. Also upon operating the release magnet M810 releases the wiper carriage of the Strowger mechanism 801; whereby it is returned to its normal vertical position reoperating the .sets of switch springs S884 and S885 and S889. More particularly, the set of switch springs S880 is operated in order to interrupt the previously traced path; for short-circuiting the lower winding of the digit absorbing relay R830; whereupon a series circuit, including the contacts 845,

Y ,M081 I, 843k and 832, is completed for energizing the lower winding of the digit labsorbing relay ,in-g operated the rotary magnet M808. y `restoring the rotary magnet M808 recompletes,

original circuit for operating the release magnet MBH). Accordingly, theA release magnet M810 restores at this time,v Also nwhen the setof switch springs S085 is operated, the secondA contacts thereof areY opened interrupting the previously traced circuit for operating the step relay R820 in order to cause the latter relay to restore; and the first contacts of the set of switch springs S885 are closed, recompleting the previously traced circuit for energizing the lower winding of the transfer relay R838 in order to cause the latter relay to reoperate. ln view of the foregoing, i t will be understood that'the toll Atransmission selector e isr of the drop-back variety and that such operation thereof proceeds in response to the Vfirst digit 2 as a consequence of the set of switch springs S889 being operated when the wiper car- Vriageof the Strowger mechanism 801 is driven two steps in the vertical direction away from its normal vertical position as described above.

The operator at the toll board 220 in the distant oiiice 10 then proceeds to dial the second digit .4; whereby the toll line circuit 400 responds thereto repeating this digit over the trunk 420to the toll transmission selector 800 in the manner explained above. In this case the wiper carriage of the Strowger mechanism 80! is driven four steps in the vertical direction away from its normal vertical position; whereby the sets of switch springs ,S884 and S885 are again reoperated.

More particularly the set of switch springs S885 step relay R820 occupy their operated positions as previously noted. Shortly following the second digit 4, the transfer relay R880 again restores completing, at this time, at the contacts 883, a

circuit, including the contacts 845, M0812, 833, and 821, for operating the rotary magnet M808; whereby the wiper carriage of the Strowger mechanism 80! is driven one step in the rotary direction away from its normal rotary position. At this time the wipers 802, etc., of the Strowger mechanism 801 engage the contact set terminatingr the nrst trunk in the group, including the trunk 240 extending to the fourth group of combination connectors including `the combination connector 235;,and the test relay R890 tests the idle or busy condition of the first trunk mentioned. v

Assuming that the rstftrunk mentioned is busy, ground potential app-ears upon the control conductor thereof completing a path for applying ground potential to the control wiper 804 of the Strowger mechanism 801l in order to complete a path, including -the contacts 06?, for shortcircuiting. the lower winding of the test relay R890 :M808 interruptaat the contacts 009, the previously traced circuit for operating thek step relay R820; whereby the latter relay restores. to interrupt, at the contacts 821, a circuit for maintain- Upon at the contacts 800, the circuit for operating the vstep relay R820; whereby the latter relay upon reoperating recompletes, at the contacts 821, the

contactsnthereof are opened, interrupting the 75 the wiper'carriagegof the'Strowger mechanism tioned, that is selected at this time. action between the stepr relay R828 and the rotary fsol an additional Step in the 'rotary direction;

whereby the test relay R898 testsfthe idle or busy condition ofthe second trunk in the group men- This inter- Inagnet M888 continues until an'idle trunk in the group mentioned is selected by the wiper set or until the wiper carriage of the Strowger mechanism 88| is driven eleven steps in the rotary direction away from its normal rotary position.

Now assuming that the trunk 248 in the group mentioned is the rst'idle trunk available to the wiper set of the Strowger mechanism 881, when the trunk 258 is selected, battery potential appearing upon Vthe control conductor thereof and Y'appearing upon the control wiper 888 of the wiper set completes a circuit, including the contacts 861, forv energizing the lower winding of the test relay R898; whereupon the latter relay operates to complete, at the contacts 898, a holding circuit, including the second contacts of the set of switch springs S885V and the contacts 841, for energizing the upper winding thereof. Also the vtest relay R888 interrupts, at the contacts 889, a further point in the circuit for operating the ystep relay R828; whereby interaction of the step ing the contacts 8 I and 855-`for applying-ground potential to the EC wiper 885 of the wiper set and consequently to the EC conductor of the trunk 288. Further the test relay R888 completes, at the contacts 88S, a path, including the contacts 871', for applying ground potential to the tone start cnd'uc'tor CSTB; and interrupts, at the contacts 895, the previously traced holding circuit for energizing the lower windingof the vvdry relay R858; however, the latter relay is retained in itsv operated position at this time Yby virtue-of a completed holding circuit for energizing the upper Winding thereof as explained more fully below. Further, the test relay R888 completes, at the contacts 88| and 892, a loop circuit, including the upper winding of the dry relay R858, to the combination connector 235. This loop circuit extends from the negative line conductor of the trunk 248 by wayfof the negative line wiper 882 of the wiper set. The contacts 885, 8L?, 852 and 882, the upper winding of the dry relay R858, the contacts 826 and 864, the lower winding 825 of the repeating coil 823, the contacts iii and 892' -and the positive line wiper 883 of the wiper set to the positive line conductor of the trunk @248; whereby a loop circuit, including 4the windings of the line relay inthe combination connector 235 and the upper' winding of the dry relay R858v is completed. Accordingly, the dry relay R858 isy retained in' its operated position and the combination connector 235 is seized; whereby it is conditioned to be responsive to the next two digits transmitted over the trunk 248.

The operator at the tolly board 228 in the distant oiiice I8 then dials the third band vfourth digits; whereby they are transmitted over the tolll line 2 I8 andl 'repeated by the toll linecircuit *488' to the'tolltraiisinissioriv selector 888; `During the third digit, the iirst time the line relay R825 restores, Yit interrupts, at theV contactsl 82T, the holding circuit' for energizing the upper winding of the digit absorbing relay R838 in order to cause the-latter relay to restore. Also during the third and fourth digits, each time the line relay R825 restores and then reoperates, it completes and then interrupts, at the contacts 828, the previously traced loop circuit extending between the upper winding of the dry relay R858 in the toll transmission selector 888 and the line relay in the combination connector 235; whereby the dry relay R858 is retained in its operated position during impulsing Since it is of the combination slow-to-operate and slow-to-release type. The line relay in the combination connector 235 follows the third and fourth digits in order to eilect operation thereof to'select the subscriber line 282 extending to the called subscriber substation T28! in the central oice 28'. The subsequent operation of the combination connector 235 depends upon the idle or busy condition of the called subscriber substation T285 at this time. When the combination connector 235 operates to select the subscriber line 282 as previously explained, the line circuit 283 is operated in order to mark the subscriber line 282 as busy to the other connectors having access thereto.

First assuming that the called subscriber substation T28l is idle at this time, the combination connector 285 switches'through in order to complete a dry loop between the called subscriber substation T28! via the subscriber line 282 and the trunk 288 to the upper winding of the dry relay R858 in the toll transmission selector 888; whereby the upper winding of the dry relay R858 is deenergized causing the latter relay to restore shortly thereafter, 'it being of the combination slow-to-operate andslow-to-release type. Upon restoring the dry relayv R858 interrupts, at the contacts 854, the previously traced circuit for maintaining operated the control relay R868; whereby the latter relay restores shortly thereafter, it being of the slow-to-release type. Also upon restoring, the dry relay R858 interrupts, at the contacts 855, the previously traced path for applying ground potential to the EC wiper 885 of the wiper set; whereby ground potential is removed from the EC conductor of the trunk 248 causing the combination connector 235 to institute the ringing operation; whereby ringing current therefrom is projected over the subscriber line 282 to the called subscriber substation T28i. Also upon restoring the dry relay R858 interrupts, at the contacts 852, the path for shortcircuiting the upper winding 825 of the repeating coil 823; reconnects, at the contacts 851, the condenser 878 to the windings 825 of the repeating coil 823; and reconnects, at the contacts 853, the condenser 828 to the windings 824 of the repeating coil 823. When the control relay R888 restores, it interrupts, at the contacts v881, the previously traced path for short-circuiting the lower winding of 'the test relay R898; and completes, at the contacts 868, a path, including the contacts Si l' and 892', for reapplying ground potential to the EC wiper V885 of the wiper set and consequently to the' EC conductor of the trunk 248 extending to the combination connector 255. Further, the control relay R888 interrupts, at the contacts '882 and 888, the connection between the rupper winding of the dry relay R858 and the windings 825 of the repeating coil 823; andrecompletes, at `the contacts 88 and 863', the normal connections between the upper Winding of 

